Chemical Reactivity S1-2-08 Objective: Relate the reactivity and stability of different families of elements to their atomic structure.
A quick review of Bohr Diagrams Number of valence electrons relates to the reactivity of an element Remember the number of maximum electrons that can go into each shell 2 in 1 st shell 8 in 2 nd shell 8 in 3 rd shell Elements want to have a full outer shell either by losing electrons or gaining them, whichever is easier! Magnesium wants to lose 2 valence electrons Metal, Metalloid, or Non-Metal? Why would Magnesium want to lose instead of gain electrons?
What happens to Magnesium if it loses 2 electrons? Will it still be Magnesium? Mg Mg 2+ Lose 2 electrons 2+ This is the ion charge How do we define an atom? Do we base the name of an atom by the number of Electrons? Protons? Neutrons? Still Magnesium! Different amount of electrons (called an ion) This means that Magnesium is missing 2 electrons!
More on Ions Non Metal! Some elements need to gain electrons to become stable Oxygen wants to gain 2 e - Oxygen would become a negative Ion When Oxygen becomes a negative ion we use the symbol O 2- Gain 2 electrons IT IS STILL OXYGEN! 2- Oxygen has become a negative ion
Two more to try! Fluorine becomes a negative ion Gain 1 electron Non-Metal Is it still Fluorine? - F - Lose 1 electron Is it still Potassium? Potassium Metal + Potassium Potassium becomes a positive ion K +
Talk with your table group Take out your periodic tables What have you noticed about the ions that Potassium and Magnesium became? Why do you think that is? What have you noticed about the ions that Oxygen and Fluorine became? Why do you think that is? Most metals want give up their valence electrons (+ ion) Most non metals want more valence electrons (- ion) Why do these atoms do this? What s the point? Atoms want to become stable! They try to do this the easiest way possible! There are some exceptions to this though Some metalloids can be + or - ions Noble gasses will never be ions Why?
Some reactivity rules All atoms want to become stable Some lose electrons (+ ion) Some gain electrons (-ion) Only electrons move! Alkali Metals and Alkaline Earth Metal will always want to get rid of their valence electrons to have a full outer shell As you go down the group reactivity increases Halogens and Chalcogens will always want to accept more electrons to have a full outer shell As you go down the group reactivity decreases Francium is more reactive than Lithium Fluorine is more reactive than Iodine
There s a catch Atoms cannot simply lose electrons unless something encourages them to do so. The same goes for gaining electrons To become stable atoms need a partner to either accept the electrons they want to get rid or if they are needed electrons they need a partner to give some up for them When atoms pair up (sometimes more atoms are needed) they form a stable substance (more on this later)
Matches made in Chemistry heaven Two Electrons are transferred from Magnesium to Oxygen Now when this transfer happens Magnesium becomes attracted to Oxygen and they form a stable compound (grade 10) We know that Magnesium wants to give up two electrons to become a positive ion and we also know that oxygen wants to get two more to become a negative ion!
Matches made in Chemistry heaven One Electron is transferred from Sodium to Chlorine Sodium Sodium loses its valence electron to become a positive ion Na + Cl - After the transfer Sodium is attracted to Chlorine and they form a stable compound! Chlorine gains an extra valence electron to become a negative ion
It s all about the number of valence electrons An atom will only achieve stability when it has a full outer shell of electrons It has to lose or gain electrons When atoms lose or gain electrons they become ions ( + or - ) Alkali Metal ions (like Sodium) love pairing with Halogens ions (like Chlorine) to become stable! Alkaline Earth Metal ions (like Magnesium) love pairing with Chalcogen ions (like Oxygen) to become stable! Hydrogen is special Since Hydrogen only has 1 shell it can only have a maximum of 2 electrons so it can gain an additional electron or lose its electron to become stable Proton + H ion - H ion
Objective: Relate the reactivity and stability of different families of elements to their atomic structure. Your Task Definitions 45 47 can be filled out! Which atom would you choose for Lithium to be a match made in Chemistry heaven? You must include Bohr diagrams for Lithium and the atom that you choose before any electron transfer. Show how the Bohr diagrams change for Lithium and your atom after the electron transfer takes places. Must be new diagrams! What type of ion does Lithium become after the electron transfer? What is its chemical symbol? What type of ion does your atom become after the electron transfer? What is its chemical symbol? 4 marks 4 marks 1 mark 1 mark 1 mark neatness 7 mark total